1. Field of the Invention
The present invention relates to a structural improvement of a coupling joint for relatively small-sized metallic and plastic tubes (hereinafter merely called "piping") 15 m/m or below in diameter or size which are arranged generally as passages for feeding oil and gas to automobiles, various kinds of machines, apparatuses and others.
2. Description of the Prior Art
As shown in FIG. 13, for example, a prior art small-size piping coupling joint of this kind comprises a joint body (21) wherein an expanded setting hole (22) consisting of a plural stepped portion and communicating with a flow hole of a connection tube wall (23) projecting ahead is perforated in a shaft center portion, and a plurality of locking holes (26) with a unified annular engaging wall (25) formed on an end circumferential wall side are perforated in a maximum-sized circumferential wall portion (24), and a tubular support member (27) wherein a back-stepped wall portion having an elastic claw wall (28) inward which engages with each locking hole (26) is stopped on the engaging wall (25) when connecting a piping (P.sub.1) so as to engage with an annular swelling wall (P.sub.1 ') provided around a connecting end portion on a side of the piping (P.sub.1) fitted close to a seal ring member inserted in a small-sized portion of the setting hole (22).
However, in such prior art, a structural complication is unavoidable from providing the elongated locking holes (26) in the circumferential wall portion (24) on a side of the joint body (21) and also the longitudinal engaging wall (25) on its end peripheral edge portion, further providing the tubular support member (27) having the elastic claw wall (28) stoppable separately at an opening on the engaging wall side, the joint must have the size longitudinal of the shaft center enlarged as a product, therefore a disadvantage is inevitable so often for use in a limited space for installation or at a portion where a complicated bend is necessary, further since the elastic claw wall (28) is engaged with the annular swelling wall (P.sub.1 ') within the joint body (21), whether or not the coupled state is proper cannot be ensured externally, and mud, dust and dirt and other foreign matters are capable of accumulating in the expanded setting hole (22).